Page 224 - Biology_F5

Coordination and Irritability

Neurones are supported, protected, and sensory neurones, intermediate neurones
nourished by non-neuronal cells of the (interneurones), and motor neurones.
nervous system, which are known as
glial cells. Together with extracellular Sensory neurones (Afferent neurones)
tissue, glial cells make up the neuroglia. Sensory neurones are characterised by
Some neuroglias are phagocytic cells long dendrites and short axons. The
FOR ONLINE READING ONLY
that remove bacteria and debris from the cell body and dendrites of the sensory
neurones while others provide metabolic neurones mostly lie outside the brain and
and structural support. spinal cord. Sensory neurones transmit
nerve impulses from sensory receptors to
Types of neurones the CNS (Figure 4.3) for the interpretation.
Based on their function and structure
there are three types of neurones, namely

Synaptic end Cell body Skin receptor
Node of
Ranvier

Myelin
sheath

Axon Direction of nerve impulse
Dendron

Figure 4.3: Structure of a sensory neurone
Interneurones (Intermediate neurones)
These are also known as connector
neurones or relay neurones (Figure 4.4). Dendrites
They are much smaller nerve cells with Cell body
many interconnections. Interneurones
have short dendrites and short or long Axon
axons. They lie entirely within the CNS
(brain and spinal cord). They transmit Synaptic ending
nerve impulses within the CNS; that is,
they relay information between sensory
and motor neurones. The sensory neurones
carry impulses towards the CNS. Figure 4.4: Structure of an intermediate neurone

Form Five Student’s Book
217